Volvox in South Africa. 609 



disagrees (1890, p. 35). Apparently Overtoil's experiments with 

 F. globator have not been repeated by any later investigator. Mainx 

 (1929, p. 210) found that parthenogenetic development of eggs is a 

 common phenomenon in F. aureus, and possibly the same may be the 

 case here, but considering the large number and vigorous nature of 

 the sperms one is chary of adopting such a view. It is possible that 

 a closer study of germinating oospores will provide a criterion for 

 determining whether a resting spore is in truth a zygote or only a 

 parthenospore. The need for observations and experiments with 

 living material is very obvious in this connection. 



Development of Oospore subsequent to Fertilisation. 



As already stated, at a certain stage of development, presumably 

 after fertilisation, the oospore rounds itself off and sinks further into 

 the parent until it lies well within the peripheral layers ; at first a 

 marked enlargement takes place, and since at this time all proto- 

 plasmic connection with the parent has ceased, this enlargement 

 must be due to the photosynthetic activity of the egg itself. Soon 

 integuments begin to form within the oogonium vesicle. The oospore 

 first lays down the spiny outer coat the outline of the dense green 

 protoplast becomes uneven (fig. 8, G), spirally arranged portions 

 project, and over them the conical spines of the outer coat form. At 

 the base of each of these projections is usually a pyrenoid. In living 

 material the green core of each spine can often be very beautifully 

 seen: in formalin-fixed material the green core may often shrink 

 away from the colourless integument, the green projections corre- 

 sponding to the outer spines then showing very clearly (fig. 8, H). 



When the spines have about reached their maximum size the 

 green projections are withdrawn, the protoplast rounds off, and the 

 inner coats are formed. These consist of a relatively thick, smooth, 

 outer coat, the mesospore, and a very delicate inner wall or limiting 

 layer, the endospore, surrounding the protoplast ; as a rule the latter 

 does not become apparent till later in the history of the oospore. 

 Janet (1912, p. 99) distinguishes only two layers in F. globator, the 

 spiny exine (exospore) and a single intine (endospore), but he 

 evidently never saw oospores germinating, when the double nature 

 of the inner coat would have become apparent (cf. Plate XLVI, G, H). 



After the formation of the integuments the colour of the oospore 

 begins to change the intense bright green gradually changes to a 

 reddish gold and ultimately to golden brown, the chlorophyll being 



